The Pyongyang skyline is rising - and not just with the trophy structures that represent the North Korean state. Despite its political and economic isolation, the capital is in the midst of a building boom.

In a comparison of photos taken by Reuters this week and on a visit to Pyongyang last October, several new high-rises of 20 or more stories have appeared in the capital, some appearing near completion.

The construction, mostly of what look to be apartments, is despite tightened U.N. sanctions against isolated North Korea for pursuing nuclear weapons and ballistic missile programs.

It is further evidence of the rising role of a market economy that has yet to be fully recognized by the government but is changing the landscape and improving the lives of people, at least in some parts of a country that remains mostly poor.

More than a dozen workers secured by harnesses on suspended platforms could be seen this week applying tile to the rough-looking concrete exterior of a low-rise building, as the capital prepared for its first ruling party congress in 36 years.

North Korea has invited foreign journalists to cover the event, but government guides restrict their movements or whom they can speak with.

Large yellow cranes could be seen jutting from the tops of taller, unfinished blocks. Red flags mark top floors.

The skyline is also getting brighter. Thanks to a surge in private solar panel use and cheap, locally-made LED bulbs, once-dim apartment windows glow, although they are still all-but drowned out by the brightly lit statues and portraits dedicated to the ruling Kim family.

The cash behind the construction comes from North Korea's version of public-private partnership. Local investors known as "donju", or "masters of money", who have earned wealth in North Korea's growing market economy, invest jointly with the state in apartment construction.

Apartment blocks in North Korea are often assigned by profession, with groups such as teachers, workers, or scientists and their families under the same roof. But a growing private trade in property and more private investors means that, as elsewhere, the best locations go to the highest bidder.

"From the perspective of the state, it's good - they can tell their people that their living standards have improved", said Lim Eul-chul, a North Korea expert at Kyungnam University in South Korea.

"Meanwhile, individual capitalists can get their apartment units after construction".

‘Energetic leadership’

The market economy appears to be growing, based on the rising number of cars on Pyongyang streets and consumer goods in shops, despite increasing isolation and the U.N. sanctions that were tightened in March following the country's fourth nuclear test in January.

At the first congress of the ruling Workers' Party since 1980, which is set to kick off on Friday, leader Kim Jong Un is expected to formally adopt his "Byongjin" policy of simultaneous pursuit of nuclear weapons and economic growth.

"Under the energetic leadership of Marshal Kim Jong Un, there's been a lot more construction in Pyongyang," said Kang Song Hui, a Pyongyang resident and guide at a children's center, invoking the leader's name as is customary when speaking to foreign journalists.

Many of the workers in the building boom are from North Korea's million-man army, with "soldier-builders" mobilized for construction and spending more time with shovels than Kalashnikovs.

They work with little modern machinery, and deadly collapses have been known to occur. In May 2014, state media reported on a rare public apology from the authorities after an apartment building collapsed, possibly killing hundreds.

A similar collapse was reported by South Korean media last month, although that has not been independently confirmed.

Bright red Chinese-made dump trucks could be seen this week ferrying rubble between building sites.

North Korean state media often touts showpiece construction projects, such as the new terminal at Pyongyang's airport or model housing sites.

The new apartment blocks rising in Pyongyang appear more grounded in economic reality than the gargantuan Ryugyong hotel, which looms over Pyongyang and has never been completed.

The 105-story pyramid-shaped structure was a barren shell for years until Egypt's Orascom was persuaded to pay for a shiny glass coating as part of a 2008 deal to set up a mobile phone network in the country.